U.S. patent number 7,704,617 [Application Number 11/730,529] was granted by the patent office on 2010-04-27 for hybrid reformer for fuel flexibility.
This patent grant is currently assigned to Bloom Energy Corporation. Invention is credited to Swaminathan Venkataraman.
United States Patent |
7,704,617 |
Venkataraman |
April 27, 2010 |
Hybrid reformer for fuel flexibility
Abstract
A reformer for a fuel cell system includes a leading segment and
a trailing segment. The leading segment includes less reactive
catalyst and/or more stabilizing catalyst than the trailing
segment. The reformer may be used for reformation of high and low
hydrocarbon fuels.
Inventors: |
Venkataraman; Swaminathan
(Cupertino, CA) |
Assignee: |
Bloom Energy Corporation
(Sunnyvale, CA)
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Family
ID: |
38559455 |
Appl.
No.: |
11/730,529 |
Filed: |
April 2, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070231631 A1 |
Oct 4, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60788044 |
Apr 3, 2006 |
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Current U.S.
Class: |
429/423;
422/626 |
Current CPC
Class: |
H01M
8/0631 (20130101); H01M 8/04097 (20130101); H01M
8/2425 (20130101); H01M 8/0625 (20130101); H01M
8/04022 (20130101); C01B 3/382 (20130101); Y02E
60/50 (20130101); C01B 2203/142 (20130101); Y02P
20/52 (20151101); H01M 2008/1293 (20130101); C01B
2203/1205 (20130101); H01M 8/2475 (20130101); C01B
2203/066 (20130101); C01B 2203/0811 (20130101); C01B
2203/107 (20130101); C01B 2203/1235 (20130101); C01B
2203/0227 (20130101); H01M 8/0247 (20130101); H01M
8/0662 (20130101); C01B 2203/1052 (20130101); H01M
8/2465 (20130101) |
Current International
Class: |
H01M
8/06 (20060101); B01J 8/04 (20060101) |
Field of
Search: |
;429/17,19,20,30
;422/190,191 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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40 05 468 |
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Aug 1991 |
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DE |
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199 24 777 |
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Nov 2000 |
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DE |
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1 057 998 |
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Nov 2003 |
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EP |
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1 571 726 |
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Sep 2005 |
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EP |
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1 258 453 |
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Jan 2007 |
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EP |
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06-104002 |
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Apr 1994 |
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JP |
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WO 00/61707 |
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Oct 2000 |
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WO |
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WO 2004/093214 |
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Oct 2004 |
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WO |
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Other References
US. Appl. No. 11/905,051, filed Sep. 27, 2007, Venkataraman. cited
by other .
U.S. Appl. No. 11/896,487, filed Aug. 31, 2007, Venkataraman. cited
by other .
Supplementary European Search Report mailed Nov. 4, 2009, received
in European Application No. 07754708.1. cited by other.
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Primary Examiner: Kalafut; Stephen J.
Attorney, Agent or Firm: Foley & Lardner LLP
Parent Case Text
This application claims benefit of priority of U.S. provisional
application No. 60/788,044 filed on Apr. 3, 2006, which is
incorporated herein by reference in its entirety.
Claims
The invention claimed is:
1. A reformer for a fuel cell system, comprising a leading segment
and a trailing segment, wherein: the leading segment comprises less
reactive catalyst than the trailing segment; the reactive catalyst
comprises nickel; a rhodium stabilizing catalyst is located in the
reformer; and the leading segment of the reformer contains a
substantially equal amount or concentration of the rhodium
stabilizing catalyst compared to the trailing segment.
2. The reformer of claim 1, wherein the leading segment contains a
lower amount of nickel than the trailing segment.
3. The reformer of claim 1, wherein the leading segment contains a
lower nickel concentration than the trailing segment.
4. The reformer of claim 1, wherein nickel amount or concentration
increases between the leading segment and the trailing segment in a
single step or in a graded fashion.
5. A fuel cell system, comprising: the reformer of claim 1; and at
least one fuel cell stack.
6. The system of claim 5, wherein: the at least one fuel cell stack
comprises an internal or an external reformation type solid oxide
fuel cells; the reformer comprises an external reformer; and the
reformer is thermally integrated with the at least one fuel cell
stack.
7. The system of claim 6, further comprising a burner which is
thermally integrated with the reformer.
8. The system of claim 5, further comprising a high hydrocarbon
fuel source and a low hydrocarbon fuel source which are fluidly
connected to the leading segment of the reformer.
9. The system of claim 8, wherein the high hydrocarbon fuel source
comprises a diesel or jet fuel source, and the low hydrocarbon fuel
source comprises a natural gas, methane, propane, ethanol or
methanol fuel source.
10. A method of reforming different fuels, comprising: providing a
reformer comprising a leading segment and a trailing segment,
wherein the leading segment comprises less reactive catalyst than
the trailing segment; providing a high hydrocarbon fuel into the
reformer, such that the fuel passes through the leading segment
before the trailing segment; providing a reformate of the high
hydrocarbon fuel into a fuel cell stack; providing a low
hydrocarbon fuel into the reformer, such that the fuel passes
through the leading segment before the trailing segment; and
providing a reformate of the low hydrocarbon fuel into a fuel cell
stack.
11. The method of claim 10, wherein the reactive catalyst comprises
nickel.
12. The method of claim 11, wherein the leading segment contains a
lower amount of nickel than the trailing segment.
13. The method of claim 11, wherein the leading segment contains a
lower nickel concentration than the trailing segment.
14. The method of claim 10, wherein: the reformer comprises an
external reformer; the fuel cell stack comprises an internal or an
external reformation type solid oxide fuel cells; and the reformer
is thermally integrated with the fuel cell stack.
15. The method of claim 11, wherein: nickel amount or concentration
increases between the leading segment and the trailing segment in a
single step or in a graded fashion; a rhodium stabilizing catalyst
is located in the reformer; and the leading segment of the reformer
contains a substantially equal or higher amount or concentration of
the rhodium stabilizing catalyst compared to the trailing
segment.
16. A fuel cell system, comprising: at least one fuel cell stack; a
reformer comprising a leading segment and a trailing segment,
wherein the leading segment comprises less reactive catalyst than
the trailing segment; and a high hydrocarbon fuel source and a low
hydrocarbon fuel source which are fluidly connected to the leading
segment of the reformer.
17. The system of claim 16, wherein the reactive catalyst comprises
nickel.
18. The system of claim 17, wherein the leading segment contains a
lower amount of nickel than the trailing segment.
19. The system of claim 17, wherein the leading segment contains a
lower nickel concentration than the trailing segment.
20. The system of claim 17, wherein nickel amount or concentration
increases between the leading segment and the trailing segment in a
single step or in a graded fashion.
21. The system of claim 17, wherein: a rhodium stabilizing catalyst
is located in the reformer; and the leading segment of the reformer
contains a substantially equal amount or concentration of the
rhodium stabilizing catalyst compared to the trailing segment.
22. The system of claim 17, wherein: a rhodium stabilizing catalyst
is located in the reformer; and the leading segment of the reformer
comprises more of the rhodium stabilizing catalyst than the
trailing segment.
23. The system of claim 16, wherein: the at least one fuel cell
stack comprises an internal or an external reformation type solid
oxide fuel cells; the reformer comprises an external reformer; and
the reformer is thermally integrated with the at least one fuel
cell stack.
24. The system of claim 23, further comprising a burner which is
thermally integrated with the reformer.
25. The system of claim 16, wherein the high hydrocarbon fuel
source comprises a diesel or jet fuel source, and the low
hydrocarbon fuel source comprises a natural gas, methane, propane,
ethanol or methanol fuel source.
Description
BACKGROUND OF THE INVENTION
The present invention is generally directed to fuel cells and more
specifically to balance of plant components, such as reformers, of
high temperature fuel cell systems and their operation.
Fuel cells are electrochemical devices which can convert energy
stored in fuels to electrical energy with high efficiencies. High
temperature fuel cells include solid oxide and molten carbonate
fuel cells. These fuel cells may operate using hydrogen and/or
hydrocarbon fuels. There are classes of fuel cells, such as the
solid oxide regenerative fuel cells, that also allow reversed
operation, such that oxidized fuel can be reduced back to
unoxidized fuel using electrical energy as an input.
SUMMARY
One embodiment of the invention provides a reformer for a fuel cell
system comprising a leading segment and a trailing segment. The
leading segment comprises less reactive catalyst and/or more
stabilizing catalyst than the trailing segment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are schematics of a fuel cell system components
according to embodiments of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
One embodiment of the invention provides a hybrid reformer for
providing fuel flexibility for a fuel cell system, such as a solid
oxide fuel cell (SOFC) system. In other words, a single reformer is
adapted to reform two or more different fuels that are used with
the system. Thus, the single reformer allows operation of the
system on multiple fuels without requiring separate reformers for
different fuels.
A fuel reformer is a device that reforms a hydrocarbon fuel into a
fuel stream comprising hydrogen and carbon monoxide. For example,
in a steam-methane reformation (SMR) reaction, steam and methane
are reformed in a reformer to a stream comprising hydrogen, carbon
monoxide and other components. A reformer may comprise a catalyst
coated fuel passage, such as a cylinder having the catalyst coated
on its interior walls and/or on an insert in the reformer housing.
The insert may comprise a catalyst coated tube, foil or wire. Other
reformer geometry, such as a rectangular passage or other polygonal
passages, may also be used.
The reformer catalyst may comprise a catalyst mixture containing
rhodium and nickel. rhodium is used for stability and nickel is
used for reactivity. Noble metals other than rhodium or in
combination with rhodium may also be used to enhance stability.
The catalyst composition is optimized for handling different fuels.
For handling high hydrocarbon fuel, such as diesel and jet fuel
(including JP5 and JP8), less nickel is used to avoid coking. For
handling lower hydrocarbon fuels such as natural gas, methane,
propane, methanol, ethanol, etc. more nickel is used.
FIG. 1 shows a preferred configuration of the hybrid reformer 109
with two segments. The leading segment 109A (i.e., the segment
where the fuel enters the reformer) from the fuel inlet conduit 127
contains less nickel for reforming a high hydrocarbon fuel, such as
diesel, and a trailing segment 109B (i.e., the segment where the
fuel exits the reformer) contains more nickel than the leading
segment for reforming low hydrocarbon fuel, such as natural gas or
methane. The trailing segment is connected to a reformed fuel
outlet conduit 153. The leading segment 109A contains a lower
amount and/or concentration of nickel than the trailing segment
109B. The reformer 109 may comprise a housing and one or more
catalyst coated inserts to form the above described low and high
nickel segments. The actual nickel amount and/or concentration in
each segment can be optimized based on the actual fuel that will be
used, the system geometry, temperature and other variables. The
reaction kinetics of higher hydrocarbons reforming to methane is
faster than the reaction kinetics of methane reforming to produce
syngas. Furthermore, the hybrid reformer can also be used together
with internal reforming type fuel cells, to allow more methane
slippage either by reducing the number of inserts or reducing the
coated area of nickel catalyst. While a sharp, single step
interface is shown in FIG. 1 between segments 109A and 109B, the
nickel amount or concentration may be graded such that it increases
monotonically or in plural steps from the inlet into segment 109A
to the outlet in segment 109B. Thus, a sharp, single step interface
between the segments is not required. Therefore, in one
configuration, the reformer contains a graded composition
increasing monotonically or in steps from segment 109A to segment
109B, with less nickel at the leading edge of segment 109A and more
nickel at the trailing edge of segment 109B. The rhodium
stabilizing catalyst amount or concentration may be substantially
constant throughout the reformer, such that the leading and
trailing segments contain substantially equal amounts of rhodium.
In another configuration, the reformer contains a constant nickel
amount or concentration throughout its length, such that the
leading and trailing segments contain substantially equal amounts
of nickel. However, in this configuration, the reformer contains
more rhodium in segment 109A than in segment 109B. The rhodium
amount or concentration may decrease from segment 109A to segment
109B in a stepwise fashion (single step or multiple steps) or it
may be monotonically graded, such that segment 109A contains a
higher amount or concentration of rhodium than segment 109B. In
another configuration, the content of both nickel and rhodium
varies between segment 109A and segment 109B. The nickel content
increases in one or more steps or monotonically from segment 109A
to segment 109B while the rhodium content decreases in one or more
steps or monotonically from segment 109A to segment 109B. Thus, the
leading segment 109A of the reformer contains a higher amount or
concentration of the rhodium catalyst than the trailing segment
109B, and the leading segment 109A of the reformer contains a lower
amount or concentration of the nickel catalyst than the trailing
segment 109B. For higher hydrocarbon fuels, such as JP5 or diesel,
a reformer containing a combination of graded nickel and rhodium
increasing in the opposite directions along the reaction path may
be used.
A method of operating the reformer 109 includes providing the high
hydrocarbon fuel into the reformer, such that the fuel passes
through the leading segment 109A before the trailing segment 109B.
The fuel is reformed in the reformer into a reformate. The method
further includes providing the reformate of the high hydrocarbon
fuel into a fuel cell stack. The method further includes providing
a low hydrocarbon fuel into the reformer, such that the fuel passes
through the leading segment before the trailing segment. The fuel
is reformed in the reformer into a reformate. The method also
includes providing the reformate of the low hydrocarbon fuel into
the fuel cell stack. Of course the order of providing the high and
low hydrocarbon fuel into the reformer may be reversed and it is
expected that the fuels may be switched several times during the
operation and/or lifetime of the reformer.
Thus, the reformer 109 may be connected to both high and low
hydrocarbon fuel sources. The high hydrocarbon fuel source may
comprise a diesel or jet fuel tank. The low hydrocarbon fuel source
may comprise a natural gas line or a fuel storage tank, such as a
natural gas, methane, ethanol, etc. storage tank. A valve or other
switching mechanism in the fuel inlet conduit 127 switches the type
of fuel being provided to the reformer 109. The valve may be
controlled by a computer or control system or manually by an
operator.
The hybrid reformer allows the fuel cell system to operate on
different fuels, such as higher and lower hydrocarbon fuels and
provides fuel flexibility including all liquid and gaseous fuels.
There is no need for having two sets of reformers depending on the
application. This reduces the reformer and system cost. The
reformer can also be used with internal reforming type fuel cells,
such as internal reforming solid oxide fuel cells.
FIG. 2 illustrates details of a portion of the fuel cell system 101
which is located in the hot box 108. The hot box 108 may contain
plural fuel cell stacks 3, such as solid oxide fuel cell stacks and
other balance of plant components, such as heat exchangers, as
described in U.S. application Ser. No. 11/002,681, filed Dec. 3,
2004, incorporated herein by reference in its entirety. Each fuel
cell stack contains a plurality of high temperature fuel cells,
such as solid oxide fuel cells. Each fuel cell contains an
electrolyte, an anode electrode on one side of the electrolyte in
an anode chamber, a cathode electrode on the other side of the
electrolyte in a cathode chamber, as well as other components, such
as interconnects which function as gas separator plates and
electrical contacts, fuel cell housing and insulation. In an SOFC
operating in the fuel cell mode, the oxidizer, such as air or
oxygen gas, enters the cathode chamber, while the fuel, such as
hydrogen or hydrocarbon fuel, enters the anode chamber. Any
suitable fuel cell designs and component materials may be used.
The fuel cells of the stack 3 may be internal reformation type fuel
cells. Fuel cells of this type contain a fuel reformation catalyst
in the anode electrode and/or in the anode chamber to allow the
hydrocarbon fuel, such as an oxygenated hydrocarbon fuel, to be
reformed internally on or adjacent to the fuel cell anode
electrodes.
Alternatively, the fuel cells may be external reformation type fuel
cells. Fuel cells of this type require that the reformer 109 be an
external reformer either because these fuel cells lack the fuel
reformation catalyst in the anode electrode and/or in the anode
chamber, or because the internal reformation catalyst may not be
able to reform a desired amount of hydrocarbon fuel. Thus, the fuel
reformation may be external or partially internal and partially
external (i.e., reformation in the reformer and in the fuel
cells).
The 109 reformer is preferably located separately from but
thermally integrated with the high temperature fuel cell stack 3 to
support the endothermic reaction in the reformer 9 and to cool the
stack 3. The system also preferably contains a burner or combustor
115. Thus, the system comprises a thermally integrated reformer
109, combustor 115 and stack 3. The reformer 109 may be heated by
the stack cathode exhaust, by radiative and/or convective heat from
the stack and/or by the combustor heat during steady state
operation.
The term "thermally integrated" in this context means that the heat
from the reaction in the fuel cell stack 3 drives the net
endothermic fuel reformation in the fuel reformer 109. As
illustrated in FIG. 2, the fuel reformer 109 may be thermally
integrated with the fuel cell stack 3 by placing the reformer 109
and stack 3 in the same hot box 108 and/or in thermal contact with
each other, or by providing a thermal conduit or thermally
conductive material which connects the stack 3 to the reformer
109.
The stack 3 generates enough heat to conduct the steam reformation
reaction in the reformer during steady-state operation of the
system 101. However, under some different operating conditions
ranging from low to high stack efficiency and fuel utilization, the
exothermic heat generated by the stack 3 and provided to the
reformer may be greater than, the same as or less than the heat
required to support the reforming reaction in the reformer. The
heat generated and/or provided by the stack 3 may be less than
required to support steam reformation in the reformer 109 due to
low fuel utilization, high stack efficiency, heat loss and/or stack
failure/turndown. In this case, supplemental heat is supplied to
the reformer. The system 1 provides the supplemental heat to the
reformer 109 to carry out the reformation reaction during steady
state operation. The supplemental heat may be provided from the
burner or combustor 115 which is thermally integrated with the
reformer 109 and/or from a cathode (i.e., air) exhaust conduit
which is thermally integrated with the reformer 109. While less
preferred, the supplemental heat may also be provided from the
anode (i.e., fuel) exhaust conduit which is thermally integrated
with the reformer. The supplemental heat may be provided from both
the combustor 109 which is operating during steady state operation
of the reformer and/or during start-up and from the cathode (i.e.,
air) exhaust of the stack 3. For example, the combustor 115 may be
in direct contact with the reformer, and the stack cathode exhaust
conduit 103 is configured such that the cathode exhaust contacts
the reformer 109 and/or wraps around the reformer 109 to facilitate
additional heat transfer. This lowers the combustion heat
requirement for the reformation reaction.
The reformer 109 may be sandwiched between the combustor 115 and
one or more stacks 3 to assist heat transfer as described in more
detail below. For example, the reformer 109 and combustor 115 may
share at least one wall or be positioned sufficiently close to each
other for radiative and/or convective heat transfer. The combustor
115 closes the heat balance and provides additional heat required
by the reformer. When no heat is required by the reformer, the
combustor unit acts as a heat exchanger. Thus, the same combustor
(i.e., burner) 115 may be used in both start-up and steady-state
operation of the system 101. When using combustion catalysts coated
on the conduit walls, the fuel may be introduced at several places
in the combustion zone to avoid auto ignition and local
heating.
In operation, a purified hydrocarbon fuel and steam mixture is fed
to the lower end of the reformer 109 through the fuel inlet conduit
127. If desired, the heavy hydrocarbon fuel, such as diesel fuel,
fuel may first be passed through a fractionator to separate the
light ends from the heavy ends, as described in U.S. provisional
application No. 60/788,044 filed on Apr. 3, 2006, which is
incorporated herein by reference in its entirety. The separated
light ends are then provided to the reformer 109 through conduit
127. A fractionator is a device which separates the shorter
hydrocarbon chain species of the high hydrocarbon (i.e., diesel or
jet) fuel from the longer hydrocarbon chain species. These are
referred to as "light ends" (predominantly C1 to C8 hydrocarbons)
and "heavy ends". The light ends are sent to a reformer. The
fractionator can be completely eliminated if the reformer can
handle higher hydrocarbons and hydrogen from anode exhaust gas
recycled prevents potential coking. The fuel may be provided into
the fractionator from a storage vessel, such as a diesel or jet
fuel tank. A non-limiting example of a fractionator is a
fractionation column, such as a distillation column containing
trays and/or packing materials, of the type used in distillation of
crude oil. The separation of the light and heavy ends in the
fractionation column occurs by distillation of different ends in
different zones of the column, with light and heavy ends being
removed from different zones of the column.
If desired, the hydrocarbon fuel may be provided directly into the
stack via a by-pass conduit 111 which by-passes the reformer 109.
The reformed product is provided from the reformer into the stack
anode (fuel) inlet 113 through conduit 153. The spent fuel is
exhausted from the stack through the anode exhaust conduit 131. Air
and fuel enters into the burner 115 via conduits 155 and 157.
The air enters the stack from air inlet conduit 159 through the
cathode (air) inlet 119 and exits through exhaust opening 121 into
the cathode (i.e., air) exhaust conduit 103. The system 101 is
preferably configured such that the cathode exhaust (i.e., hot air)
exits on the same side of the system as the inlet of the reformer
109. For example, as shown in FIG. 2, since the mass flow of hot
cathode exhaust is the maximum at the lower end of the device, it
supplies the maximum heat where it is needed, at feed point of the
reformer. In other words, the mass flow of the hot air exiting the
stack is maximum adjacent to the lower portion of the reformer
where the most heat is needed. However, the cathode exhaust and
reformer inlet may be provided in other locations in the system
101, such as to a steam generator. If desired, the hot combustor
115 exhaust may be provided into the steam generator through
conduit 117 to heat the water in the generator to generate steam.
The combustor exhaust may be provided into the steam generator in
addition to or instead of one or more exhaust streams from the fuel
cell stack 3.
The foregoing description of the invention has been presented for
purposes of illustration and description. It is not intended to be
exhaustive or to limit the invention to the precise form disclosed,
and modifications and variations are possible in light of the above
teachings or may be acquired from practice of the invention. The
description was chosen in order o explain the principles of the
invention and its practical application. It is intended that the
scope of the invention be defined by the claims appended hereto,
and their equivalents.
* * * * *